Roy Mustang was able to heal himself, analyze his opponent and counter attack. Mustang spoke confidently that he had figured out her attack and knew how to kill her. After the first of his many assaults, Lust's attitude had changed to fear and rage at the fact that Mustang had indeed figured out her weakness and that she was going to die beyond any shadow of a doubt. It can be said that at this point, the tide of battle turned in a severely lopsided way and Mustang began to pwn his opponent.

... and begins his pwnage.

So yes, while rare, a person can sustain serious injury but still pwn their opponent. Some of the usual traits of these situations are battles where one person has an unpredictable ability that will give them an upper hand until their opponent is aware that they have said ability.